Electronic tone generator



Jan. 7, 1958 R. E. WILLIAMS 2, 1 61 ELECTRONIC TONE GENERATOR Filed March 21, 1950 4 Sheets-Sheet 1 FIG. 2

INVENTOR A'T'roRNEYs Jan. 7, 1958 R. E. WILLIAMS ELECTRONIC TONE GENERATOR 4 Sheets-Sheet 2- Filed March 21 1950 Jan. 7, 1958 R. E. WILLIAMS 2,818,761

ELECTRONIC TONE GENERATOR Filed March 21, 1950 4 Sheets-Sheet 3 HG. 7 I 52 ATTORNEYS Jan. 7, 1958 R. E. WILLIAMS 2,818,761

ELECTRONIC TONE GENERATOR Filed March 21 1950 4 Sheets-Sheet 4 FIG. 9 FIG. I2 68\ /e9 e 1 FIG. 64 65 I INVENTOR A'II'TORNEYS United States PatentO ELECTRONIC TONE GENERATOR Richard E. Williams, Manchester, N. H., assignor to Wilbespan Research Labs, Inc., Manchester, N. H.

Application March 21, 1950, Serial No. 150,892

-Claims. (Cl. 84-115) This invention relates to improvements in electronic tone generators generally, and more particularly to improvements in electronic tone generators of the type described in detail in my United States patent application, Serial No. 44,697, filed August 17, 1948, now Patent No. 2,681,584 issued June 22, 1954 and in my United States patent application Serial No. 74,388, filed February 3, 1949, now Patent No. 2,588,680 issued March 11, 1952.

The type of musical instrument therein described comprises in etfcct a light source separated from a light cell by a moving screen having a light modifying action. The nature of this screen, which may be in the form of a disc or cylinder containing endless soundtracks, determines the nature of the voltage produced by the cell. This voltage, in turn, is ltransduced to sound by suitable means. Shutters controllably masking soundtracks provide operable means for producing the tones singly or in combination.

By the present invention clearer production of tones with minimum inter-soundtrack interference, additional enhancing effects, clearer production of tones, and simpler operation are obtained.

An object of the present invention is to provide a tone generator of the semi-mechanical type in which frequency vibrato is simultaneously and simply applied to all tones of an equally tempered scale impressed upon a tone wheel.

Another object is a method of speed-translation which makes possible an independent tone-wheel speed, yet.'provides means of causing inherent or desired variations in soundtrack parameters to occur at a natural vibrato rate.

Again, the invention will be found to reside in a simplified method of introducing periodic variations in speed of a .tone wheel at any desired rate.

Further, the invention has for its object means for minimizing key-click and noise as a result of abrasions, etc. of a photo-electric tone wheel.

The foregoing and other objects will manifest them selves as the following description progresses, references being bad to the accompanying drawings, in which:

Fig. 1 is a view of eccentric meshed gears;

Fig. 2 is a view of a light collimating and separating device;

Fig. 3 is an elevational view partly in section, of a drive means .providing for periodic speed variation;

Fig. 4 is a plan view of a modified drive means;

Fig. 5 is a typical push-pull soundtrack with typical scanning slits;

Fig. 6 is a light dividing and separating device to be used with push-pull soundtracks;

Fig. 7 is a semi-diagrammatic view of the masks shown in Fig. 6;

Fig. 8 is a typical soundtrack with scanning slit locations;

Fig. 9 is an endless soundtrack disc showing start-end spot location;

Fig. 10 is an enlarged view of atypical start-end spot;

2,818,761 Patented Jan. 7, 1958 Fig. 11 is an enlarged view of a typical false start-end spot;

Fig. 12 is an endless soundtrack disc showing start-end spot and false start-end spot locations; and

Fig. 13 is a plan view of a further modification of the drive means.

In the case where all pitches of an equally tempered scale are recorded upon a single tone wheel it has been shown that problems resulting from attempts to join the start and end of an endless soundtrack are greatly minimized by causing these start-end spots to occur at a natural vibrato rate commonly considered to lie between the frequencies of four and twelve times a second. More generally stated, undesirable variations in any of the parameters associated with soundtrack creation will be psychologically minimized in respect to their distracting qualities if they are caused to repeat themselves at a natural vibrato rate.

As an additional means of enhancing substained tones of the recorded type it is desirable to vary their pitches periodically about a mean value at the same vibrato rate.

A simple method of obtaining a pitch variation in the case of a tone wheel is shown in Fig. 1, wherein a driving gear 1 aifixed to a relatively constant speed shaft 2 is eccentrically meshed with a driven gear 3 aifixed to a driven spindle 4. Assuming the driving shaft 2 to be rotating at a natural vibrato rate, the driven spindle 4 will vary above and below a mean speed at the vibrato rate. If the two gears 1 and 2 are similar in diametral pitch, pitch diameter, and eccentricity percentage, they will remain in proper mesh as can be seen by noting that meshing radii 5 and 5 have an additive equivalent to arbitrary meshing radii 6 and 6. It is necessary to interpose the pair of eccentric gears 1 and 3 into a speed translation chain between a motor and tone wheel wherein their average speed is in the order of a natural vibrato rate to obtain tone wheel pitch variations at the same vibrato rate. It is readily seen that because fixed meshed gears are used in the system shown in Fig. 1 that no slippage between the driving shaft 2 and driven spindle 4 is possible. Under such a situation it is possible to use a very constant speed source such as a synchronous motor coupled as described to a tone wheel wherein variations in speed other than those desired at a periodic rate are completely eliminated.

An alternate method of obtaining a periodic variation of speed in a tone wheel wherein it is unnecessary to use a member rotating at a natural vibrato rate is shown in Fig. 3. A driving shaft 7 is coupled through resilient means 8 to a driving gear 9. The driving gear 9 is meshed to an intermediate gear 10 with respective pitch diameters being made such that the intermediate gear 10 cycles at the natural vibrato rate or a sub-multiple thereof. For instance, if a vibrato rate of 6 cycles per second is desired, the intermediate gear 10 may rotate at a speed of 6 cycles per second, 3 cycles per second, 2 cycles per second, or any integral sub-multiple of 6 cycles per second. The intermediate gear 10 has aifixed to it an irregularly shaped cam 11 with projections 12 and 13 being in number the multiple of the intermediate gear speed required to get the above mentioned vibrato rate. In the case shown, the intermediate gear 10 can be as sumed rotating at 3 cycles per second. Two projections 12 and 13 on the irregularly shaped cam 11 pass a brake 14 once a revolution or three times per second each, with a resultant braking action occuring at the desired vibrato rate of six times per second. Because the brake 14 exerts torque variation periodically at the vibrato rate the intermediate gear 10 is retarded and accelerated at this rate along with the driving gear 9, the difierence in speed between the driving gear 9 and the constant speed driving shaft 7 being absorbed by the resilient coupling means 8. A driven gear 15 afiixed to a tone wheel spindle 16 has a pitch diameter such that the tone wheel spindle 16 is driven at any desired rate, but will be periodically varied in speed at the vibrato rate calculated as described. It is important to realize that although the average speed is translated in proportion to pitch diameter ratios, the frequency at which variations in speed are introduced is not varied. The percentage of speed deviation is subject to translation in proportion to subsequent gearing ratios, but may easily be controlled by adjusting the braking or retarding torque itself in compensation.

For instance, if an eventual speed deviation of i2% is desired in the tone wheel spindle 16 in Fig. 3, and the ratio of pitch diameters of the intermediate gear and the driven gear is 2 to 1; the brake 14 must exert sufiicient change in torque to provide the intermediate gear 10 with a :l% Variation in speed. This variation is brought to 2% by the gear step up in speed. The rate at which the variation re-occurs, on the other hand, is not affected in any way by the speed step up. A simple way to realize this is to consider that if a motor driving a gear chain is started and stopped, the final driven gear also starts and stops just once regardless of intermediate gearing ratios. The actual variation in speed of the final driven gear is, however, dependent upon the gearing ratios.

It will be noted that this system provides means for providing a vibrato rate speed fluctuation to a tone wheel with an average speed which may be dictated by the tone wheel itself. Again, variation in braking torque caused by varying the effective tension of the brake 14 will vary the percentage of speed fluctuation without varying the average tone Wheel speed and dependent tone pitch.

A simple application of the principle is shown in Fig. 4 wherein a constant speed motor 17 is coupled through resilient means 8 to a driving gear 9, in turn meshing an intermediate gear 10. A brake 14 rides an irregularly shaped cam 11 in such manner that all cycling members following the resilient coupling 8 in the entire driving chain vary periodically about a mean speed. The speed translation between a second intermediate 17' and a driven spindle gear 15 is calculated to provide the tone wheel 13 with an average speed most expedient to proper production of desired pitches.

Also, it is possible to use the arrangement shown in Fig. 13, in which a relatively constant speed. source 60 is coupled to a tone wheel 18 through resilient means 8'. A brake 14 and an irregularly shaped cam 11' provide an irregular retarding torque to the tone wheel 18 through the gears 17 and 15. The calculations regarding braking torque, etc., are essentially similar to those indicated in reference to Figs. 3 and 4, the only differences being in gear train arrangement.

In the case of a tone generator in which the tone wheel is in the form of a photo-electric light screen containing endless soundtracks, sub-multiple vibrato operation can be used to great advantage. Referring to Fig. 9, the tone wheel 61 has imprinted upon it an endless soundtrack 62 which has a discrepancy 63 imposed upon the soundtrack 62 at the time of recording as a result of the start-end spot. Referring to Fig. 10, the recorded waveform 64 approaches the start-end spot 65 in a diminishing manner, then rises to full amplitude slowly reaching its full modulation value 66. Simultaneously with the amplitude variation shown it is usual for a phase shift to occur. If the phase shift is disregarded it is possible to simply record the waveform shown as 67 in Fig. 11. This wave series whose decline 68 and rise 69 are electronically controlled can be incorporated into the waveform sequence at any point in the endless soundtrack 62 in Fig. 9. In the case where one rise-fall point 63 occurs it is desirable to operate the light screen 61 at a speed equivalent to the natural vibrato rate in such a manner that the rise-fall spot will be scanned at that rate.

If, however, an additional rise-fall point 70 in Fig. 12 were recorded diametrically opposed to the inherent risefall or start-end spot 63, it is then advisable to cycle the light screen 61' at a speed equivalent to the natural vibrato rate divided by 2, in such a manner that the risel'all spots, either inherently or intentionally recorded 70 and 63, will be effectively recurrent at the natural vibrato rate. Generally stated, the tone Wheel upon which the endless soundtracks are inscribed should cycle at the natural vibrato rate desired divided by the number of rise-fall spots on an endless soundtrack.

It is to be understood that although a photo-electric light screen is used for purposes of illustration, any tone wheel upon which discrepancies are to be found may have distracting manifestations minimized by operating it at a sub-multiple of a vibrato frequency calculated in the manner described.

Another improvement that can be applied to tone generators of the photo-electric type in which a series of soundtracks is recorded upon a rotating tone wheel, and independent shuttering means is provided for exposing said soundtracks is shown in Fig. 2. It is desired in a tone generator of this type that interference or light leakage between adjacent soundtracks be held to an absolute minimum. If such restrictions are not imposed, operation of a shutter will result in not only the desired tone but in addition some of the unselected tones created by the soundtracks on either side of the desired one. Referring to Fig. 2, a light source 19 is placed at the focal point of a parabolic reflector 20 in such manner that light rays 21 are effectively collimated into parallel beams. In the path of these collimated beams are placed a series of independently controllable shutters 22. The shutters are made sufiiciently long in the direction of the light beam and are channeled in such manner that overlapping wings 23 effectively block off all light attempting to reach the photo cell 24. If a shutter is lifted a vacancy exists in the series of shutters shown as 25 in Fig. 2. The proximity of the wings of adjacent shutters 23' and 23 together with the collimated light beam 26 insure that little or no lateral dispersion of light can occur, resulting in clear definition of individual soundtracks. It has been found that it is extremely difficult to prevent light leakage unless both collimation and overlapping condition such as that shown in Fig. 2 are provided. It is to be understood that the light collimating device can occur in other forms such as the conventional application of lenses, defraction gratings, etc.

Another improvement in a photo-electric tone generator of the type just described is indicated in Figs. 5, 6, 7, and 8. More specifically referring to Fig. 8, that of a conventional soundtrack, it will be seen that with a modulated soundtrack the opening of a shutter normally masking such a track will result in an average light increase of 50%. This can be explained by first assuming that a closed shutter permits zero light transmission. When the shutter is open, however, the passing track 27 leaves variations in respect to time which can be considered full light 28, zero light 29, and intermediate steps 30. It can be realized that the average light transmitted in such a case will lie half way between the maximum light condition 28 and the minimum condition 29 or a 50% light transmission average. In the case of a musical instrument when the shutters are controlled by keys, opening and closing of shutters as described will result in a certain amount of so-called key-click. Although not extremely annoying because of its inherent similarity to attack noises of many wind instruments, it may be desirable in some cases to minimize this click resulting from an increase in the average value of transmitted light or D. C. component. A method of eliminating this can be understood with specific references to Figs. 5, 6, and 7. Referring to Fig. 5, a special sound track known as a pushpull type track 31 is seen to have the same percentage of light transmission regardless of where it is scanned as shown by scanning slits 32, 33, and 34. With conventional scan, therefore, little or no signal output would be heard upon track exposure, the average light transmitted being constant. Key-click would still be apparent upon opening of a shutter as the average light will upon exposure jump from zero to a finite value dependent upon the clear width 35.

If, however, it were possible to scan the left and right sides 36 and 37 independently, an unusual situation results. If the track were in such a position as to give that exposure shown in slit 32. it is noticed that the left hand scan 38 results in zero light transmission whereas the right hand scan 39 results in maximum light transmission. The condition is just opposite in the scan 34 where the left hand side 40 provides maximum light and the right hand side 41 provides minimum light. Between these two conditions there lies a point of scan 33 in which each side transmits 50% of the total light. It can be noticed that the right hand side progresses from a maximum light transmission 39 through a 50% transmission point 42 to a Zero transmission point 41. A signal is therefore apparent if the right hand side of the track were scanned alone. The left hand side goes from a zero point of transmission 38 through a 50% transmission 43 to a maximum transmission point 40. The left hand side, therefore, produces a signal also, although this signal is reversed to that of the right hand side in respect to time. In cyclic measure the two track halves may be said to be 180 out of phase.

A method of scanning the left and right halves of each soundtrack with discrete photo-electric cells is shown in Fig. 6. In this case the light beam 44 penetrates the soundtrack 45 and impinges upon the surface of a semireflective optical device 46. A surface 47 reflects 50% of the light beam upward as shown by lines 48 through a mask 49 to a photo-electric cell 50. The other 50% of the total light penetrates the optical device 46 as shown by lines 51 through a mask 52 to another photo-electric cell 53. The masks 49 and 52 in Fig. 6, are more graphically shown with reference to Fig. 7. It will be noted that each mask has a series of apertures 71 positioned in such a manner that halves of projected soundtracks 54 and 55 are scanned by one or the other of the discrete photo cells 50 and 53 in Fig. 6. Lateral adjustment one to the other of the masks 49 and 52 provide means for selecting the soundtrack halves to be scanned by the discrete cells.

Referring again to Fig. 6, the photo cells 50 and 53 are connected in push-pull through suitable means such as a transformer 58. Because they are connected to opposite ends of the primary winding 57 of the transformer 58, the secondary 59 of the transformer 58 will respond only to the difference in electrical output of the photo-electric cells 50 and 53. Referring again to Fig. 5, it will be noted that because of the phase opposition of the two halves of the soundtrack, a large signal output will be obtained with a push-pull electrical connection. However, because opening of the shutter brings the average light transmitted to each of the discrete cells to 50% of its maximum value, this average or D. C. component will be completely cancelled because of its in-phase characteristic. The key-click resulting from average light variations, therefore, is eliminated.

In the case of intentional amplitude variations, recorded to eliminate phase discrepancies as described in my United States patent application, Serial No. 74,388, filed February 3, 1949, this multiple cell and masking combination greatly minimizes the audible manifestations resultant.

It will be apparent to those skilled in the art that numerous other variations and modifications of the invention may be made without departing from the underlying principles thereof. For instance, tone wheels consisting of metallic discs with peripheral projections may easily utilize substantially the basic methods and combinations described herein. I therefore desire, by the accompanying claims, to include within the scope of my invention all such variations and embodiments as will readily occur to those skilled in the art and by which substantially the results of my invention may be obtained by substantially the same means.

What is claimed is:

1. A tone generator having a cycling tone member and an endless sound track on said tone member, said sound track having a first discrepancy at a start-end spot of waveform generation thereon, and said sound track having included in its length at least one additional discrepancy substantially similar to that of said start-end spot, said first and additional discrepancies being substantially equally spaced along the length of said sound track, and means for cycling said sound track at a speed equal to a vibrato rate divided by the total number of said discrepancies.

2. A tone wheel having an endless waveform modulated soundtrack, said waveform having a start-end region of generation and a phase amplitude discrepancy thereat, and at least one similar additional discrepancy in said waveform, said start-end and additional discrepancies being spaced substantially equally along said soundtrack, and mean for rotating said tone wheel at a speed equal to a vibrato rate divided by the total number of said discrepancies.

3. In a tone generator, the method of masking a startend discrepancy in the waveform of an endless soundtrack by means of a vibrato recurrent effect while enabling scanning of the sound track at less than a vibrato speed, which comprises providing the soundtrack in efiect with additional discrepancies similar to said start-end discrepancy with the plural discrepancies substantially equally spaced along said soundtrack, and scanning said soundtrack at a rate in soundtrack lengths per second equal to a natural vibrato rate divided by the total number of said plural discrepancies.

4. In a photoelectric tone generator, a light modulating tone screen having an endless waveform modulated soundtrack with a start-end discrepancy in said waveform and at least one similar waveform discrepancy, said discrepancies being spaced equally along said soundtrack, and drive means adapted to cycle said tone screen at a rate in soundtrack lengths per second equal to a natural vibrato rate divided by the total number of said discrepancies.

5 In a tone generator, an endless waveform modulated soundtrack having a plurality of similar discrepancies substantially equally spaced along the length of the soundtrack, one of said discrepancies comprising a waveform start-end spot phase shift, and means adapted to scan said soundtrack at an average speed in soundtrack lengths per second equal to a natural vibrato rate divided by the total number of said discrepancies.

References Cited in the file of this patent UNITED STATES PATENTS 1,319,820 Kent Aug. 18, 1931 22 Potter Mar. 8, 1932 1,991,522 Ranger Feb. 19, 1935 2,588,680 Williams Mar. 11, 1952 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,818,761 January '7, 1958 Richard Ea Williams It is herebfl certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 19, for 'substained" read sustained e; column 6,

line 30, for "mean" read means "a Signed and sealed this 9th day of September 1958.,

(SEAL) Attest:

KARL H. AXLINE ROBERT C, WATSON Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,818,761 January 7-, 1958 Richard E a Williams It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 19, for 'substained" read sustained e; column 6,

line 30, for "mean" read means Signed and sealed this 9th day of September 1958,

(SEAL) Attest: KARL H, AXLINE ROBERT (J. WATSON Attesting Oflicer Commissioner of Patents 

